Aqueous absorption fluids

ABSTRACT

The rate of water vapor sorption of an absorption cycle cooling and/or heating system using an aqueous alkali metal halide or hydroxide solution as the working fluid is increased by adding to the fluid an effective additive amount of at least 2 parts per million of a primary, secondary or tertiary aliphatic, cycloaliphatic, heterocyclic or aromatic amine to the fluid capable of increasing the rate of water vapor absorption.

This application is a continuation-in-part of application Ser. No. 08/180,712 filed Jan. 13, 1994, U.S. Pat. No. 5,419,145.

BACKGROUND OF THE INVENTION

In the aforesaid co-pending application, there is disclosed the use of amines as additives for improving and increasing the rate of water vapor absorption in absorption cycle cooling and/or heating systems. In the aforesaid application, the working fluid is an aqueous alkali metal hydroxide solution. The present invention includes the use of amines as effective additives in aqueous absorption working fluids where other metal salts are used in the absorption solution.

SUMMARY OF THE INVENTION

According to the present invention primary, secondary and tertiary aliphatic, cycloaliphatic, heterocyclic and aromatic amines are highly effective heat and mass transfer additives in aqueous metal salt and alkali metal hydroxide solutions used in water vapor absorption cycle systems. The presence of such amines increases the rate of water vapor absorption by the aqueous metal salt absorption fluids thereby achieving important advantages and improvements in system performance. The improvements include absorber power load increases and improvements in the change of absorber fluid concentrations. Further improvements include increase in overall heat transfer coefficients and sorption fluid side film heat transfer coefficients. The advantage of such improved absorption fluid performance allows for reduction of sorber heat exchange surface areas needed to satisfy a given load resulting in reduction of absorber size and costs. These and other improvements and advantages will be evident from the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The specific improved aqueous absorption solutions used in the systems of the present invention are aqueous solutions of metal salt or alkali metal hydroxide solutions in which water is substantially the only solvent. By this description, it is intended to exclude those solutions containing additional solvents such as glycols, polyglycols, alcohols, glycol ethers, glycerol and the like in solvent amounts. The preferred metal salts are alkali metal halides, particularly lithium bromide, lithium chloride and lithium iodide and mixtures of two or more of them. The most preferred working fluid is an aqueous solution of lithium bromide as the only absorbent present in the aqueous solution. However, in addition to the preferred lithium bromide, one or more of the following salts may also be present: ZnCl₂, ZnBr₂, MnCl₂, MnBr₂, MgCl₂, MgBr₂, SrCl₂, SrBr₂, CaCl₂, CaBr₂, FeCl₂, FeBr₂, LiCl, LiI, LiNO₂, LiNO₃, LiSCN and LiClO₃. The amount of salt present, whether lithium bromide alone or a mixture of two or more of the aforesaid salts is preferably between about 40% and about 85%, by weight. However, the presence of calcium in the absorption fluid may cause precipitation of some amines which may make such systems unattractive. The aforesaid LiBr aqueous absorption solutions are well known to those skilled in the art as disclosed, for example, in U.S. Pat. No. 3,478,530.

The alkali metal hydroxide absorption fluids are aqueous solutions of sodium hydroxide, potassium hydroxide or mixtures thereof. Preferred hydroxide compositions are those utilizing a mixture of the two hydroxides, and preferably those in which the total hydroxide concentration is between about 30% and about 80%, by weight. It has been found that optimum energy storage potentials are realized when sodium hydroxide is present between about 35% and about 75%, by weight, of the combined sodium hydroxide and potassium hydroxide weight. The amount of sodium hydroxide present in the salt mixture for systems at crystallization temperatures above 30° C. is 50% or above, whereas for temperatures below 30° C., the preferred amount of sodium hydroxide is at or below 50% of the salt mixture. The most preferred amount of sodium hydroxide is between 40% and 55% of the combined weight of sodium hydroxide and potassium hydroxide for crystallization temperatures below 30° C. In addition to the aforesaid sodium and/or potassium hydroxide solutions, relatively small amounts of other alkali metal hydroxides may be added as well. Thus, the hydroxide solutions may contain up to about 10-15% cesium, rubidium, and/or lithium hydroxide, based on the weight of sodium and/or potassium hydroxides.

The heat and mass transfer additives of the invention are primary, secondary or tertiary aliphatic, cycloaliphatic, heterocyclic or aromatic amines. Preferred amines are those that are normally liquid at system operating conditions, for example, between about 30° C. and up to 100° C. or more. Additives of the present invention may be used in systems with absorber temperatures of about 20° C. or less if they are selected from those amines with a melting point less than the absorber temperature. The additives may be liquid over a wider temperature range, both higher and lower, without adversely affecting the operation of the invention. Thus, for example, aniline is a satisfactory additive, with a freezing point of -6° C. and a normal boiling point of 184° C. The amines may contain one amine functional group, or may have multiple amine groups including two, three or more functional groups in the same molecule. Preferred amine additives, according to the invention, are aliphatic and aromatic amines, preferably having between four and twenty and more preferably between six and twelve carbon atoms. For the alkali metal halides, and particularly the lithium bromide solutions, the most preferred amines are ethylhexylamine, N,N-dimethyloctylamine, aniline and benzylamine. Other examples of useful aliphatic amines include tert-octylamine, n-octylamine, di-sec-butylamine, pentylamine, butylmethylamine, dipropylamine, butylethylamine, triethylamine, pentylethylamine, hexylamine, cyclohexylamine, trans-1,2-diaminocyclohexane, N,N-diethylcyclohexylamine, 1,5-dimethylhexylamine, N,N-dimethylhexylamine, N-methyldibutylamine, nonylamine, N,N,diisopropylethylamine and 2-methyl-1,5-diaminopentane and others disclosed in the aforesaid application and incorporated herein by reference. A most preferred amine additive for the lithium bromide absorption solutions of the invention is 2-ethylhexylamine. Other preferred primary amines include cycloaliphatic or alicyclic amines such as cyclohexylamine and diaminocyclohexane and its different isomers. Other particularly useful and effective amines include secondary aliphatic and saturated cyclic or heterocyclic amines of 4-12 carbon atoms such as dialkylamines, piperidine and substituted piperidines, and pyrrolidine and substituted pyrrolidines. Preferred derivatives are alkyl or halogen substituted. Another preferred group of amines include tertiary aliphatic and saturated heterocyclic amines such as N,N-dimethytoctylamine, N,N-diethyloctylamine, N,N-disopropylethylamine, and N-methylpiperidine. Another useful group are the aromatic amines such as aniline, and substituted anilines such as 3,5-bis-trifluoromethylaniline, 2,3,4,5,6-pentafluoroaniline, and the different isomers of toluidine and anisidine. The aromatic amines may be polycyclic such as α-naphthylamine and β-naphthylamine, and alkyl substituted napthylamines. Unsaturated heterocyclic and aromatic nitrogen compounds such as quinoline, isoquinoline, pyrrole, pyrroline, and pyridine, and alkyl and halogen-substituted heterocyclic aromatics, particularly methyl and fluorine substituted derivatives, are also useful and preferred additives of the invention. Other active nitrogen compounds included aliphatic and aromatic nitriles such as benzonitrile, tolunitrile, and octylnitrile.

From the aforesaid specific examples, it will be noted that the amino compounds may have one or more amine functional groups in the same molecule. However, not all polyfunctional amine additives will be active with all fluids. Particularly for lithium containing solutions, it is important to avoid additives that form a chelation complex with the cations of the absorbent thereby reducing or preventing heat and mass transfer activity. For example, 1,2-diaminocyclohexane can form a five-membered ring in LiBrH--H₂ O, consisting of the lithium atom, the two amine nitrogen atoms, and carbon atoms number 1 and 2 on the cyclohexane ring. Thus, five, six and seven-membered rings are to be avoided with lithium. The tendency toward chelate formation with additives is more prevalent with LiBr solutions than with metal hydroxide solutions such as NaOH--H₂ O. For example, while 1,2-diaminocyclohexane is an active additive for NaOH and KOH solutions, and mixtures thereof as shown in application Ser. No. 08/180,712, it is not active with LiBr--H₂ O solutions. The capability of a polyfunctional additive to form such rings will be obvious to those practitioners skilled in the chemical art. The amine molecule may also include one or more other functional groups such as alcohols, halogens, thiols, ethers, and ketones, provided such functional groups do not cause the amine to form a precipitate or otherwise induce chemical instability in the presence of the metal halide or hydroxide solutions. It is also to be understood that the specific amines disclosed are given by way of example only, and any of the aforesaid amines or combinations thereof within the disclosed groups of amines may be used.

The effective additive amounts of amine additive added to the aqueous salt solutions for the purpose of improving heat and mass transfer is from at least about two parts per million and preferably up to about 20,000 ppm, by weight. Preferred concentrations are between about 2 ppm and 10,000 ppm and more preferably between about 5 ppm and about 5,000 ppm, although amounts in excess of this range up to 20,000 ppm or more will not adversely affect the system operation. Mixtures of the aforesaid amine additives may also be used. In addition to mixtures of the amines other known additives such as 2-ethylhexanol may also be added where a mixture of additives is desired or where another additive such as 2-ethylhexanol is already present in the absorption fluid.

According to the invention, it has been found that the presence of an amine in the aqueous absorption fluid containing a lithium halide or the sodium or potassium hydroxides, or mixtures of the hydroxides results in substantially improved heat and mass transfer performance of the absorption working fluid composition. Specifically, the performance of the system improves in the following manner: water cooling temperature change in the absorber, for a constant water flow rate, rises significantly; the absorber power load increases proportional to the change in water cooling temperature; the steady state vapor pressure drops, and if brought back to its initial value to achieve a constant evaporator temperature, the change in concentration of the absorber fluid increases significantly; the absorber solution subcooling, i.e., the difference between the maximum temperature at equilibrium (saturation) and the actual solution temperature, is decreased by several degrees; the absorber solution-heat exchanger tube interface comprises a highly agitated turbulent film as compared to a generally laminar flow pattern without presence of the additive; and overall heat transfer coefficients and sorption fluid film heat transfer coefficients are increased.

As previously noted, water vapor absorption systems incorporating the amine heat and mass transfer additives in the aqueous alkali metal absorption solutions of the invention include a number of different types of systems incorporating one or more absorbers in which water vapor absorption solutions are typically used. Such equipment includes absorption chillers and refrigeration systems as disclosed in U.S. Pat. Nos. 4,966,007, 5,038,574 and 5,186,009, thermal energy storage systems as disclosed in U.S. Pat. No. 4,823,864, as well as multiple effect absorption refrigeration systems, for example, double effect and dual loop systems disclosed in U.S. Pat. Nos. 3,266,266 and 4,542,628 and triple effect systems disclosed in U.S. Pat. Nos. 5,335,515 and 5,390,509. The description of the apparatus and systems disclosed in the aforesaid application and patents are incorporated herein by reference. Especially preferred are the single and double effect absorption chiller and refrigeration systems which includes those systems in which the single or double effect components are a portion of the system, such as a dual loop triple effect system comprising combined single stage loops as disclosed in U.S. Pat. No. 4,732,008. The aqueous working fluids of the invention may also contain a corrosion inhibitor such as chromates, nitrates, tungstates or molybdates, as disclosed for example in U.S. Pat. Nos. 5,186,009 and 5,335,515 or other suitable corrosion inhibitors.

To illustrate the improvement of system performance by using the heat and mass transfer additives of the present invention, the following examples are provided. In the Table, amine additives within the scope of the present invention are shown by way of example. The results given are for a constant set of operating conditions and include: initial cooling water ("Tube") temperature of 30° C., a system water vapor pressure of 10 mbar, 7° C. dew point (evaporator temperature), initial aqueous solution concentration of 60% LiBr, initial solution flow rate of 400 grams/min, and initial solution temperature of 48° C. entering the absorber, using a special bench test absorption machine. The solution flow rate used for nonylamine is 300 grams/min and for pyridine 500 grams/min. The water and solution temperatures, flow rates and vapor pressures are taken from monitor readings during operation. The concentrations are determined from fluid samples taken from the machine.

The results are based on heat transfer equations well known to practitioners of the art. The absorber load dQ/dt, shown as W, is calculated from the water temperature, heat capacity of water, and water flow rates, ##EQU1## For the heat transfer coefficients, the temperature change is treated as the log mean differential temperature, where ##EQU2## The outside film heat transfer coefficient h_(o) is calculated from ##EQU3## and where R_(i),m is the thermal resistivity of the inside cooling water and copper metal tube wall. Solution subcooling is the temperature difference (ΔT) between the actual solution temperature leaving the absorber and the calculated absorber solution equilibrium temperature at the measured concentration and system vapor pressure values. Thus, lower subcooling temperature values reflect greater system efficiency as do increased outside film heat transfer coefficients, h_(o). The value calculated for solution subcooling is one measure of the efficiency of the system for water vapor absorption, with lower subcooling temperatures indicating an improvement. However, under certain conditions, the derived subcooling numbers may be contrary to other direct measurements of water vapor absorption. In the Table some data show higher calculated solution subcooling while also showing increased water vapor absorption rates by increases in absorber loads, and increases in heat transfer coefficients. Thus, the derived subcooling results are to be checked against other direct evidence of increased absorption rates.

                  TABLE                                                            ______________________________________                                                                Load   ho     Subcooling                                Additive       ppm     W      W/m2K  °C.                                ______________________________________                                         nonylamine     0        417   1099   9.4                                                      0        512   1291   7.1                                                      0        540   1595   6.6                                                      15.7     563   1208   6.4                                                      15.7     509   1092   5.4                                                      26       678   1535   5.5                                                      26       671   1610   5.1                                                      36       760   1651   4.2                                                      36       752   1588   3.6                                                      46       787   1570   3.1                                                      46       780   1676   5.0                                                      56       780   1619   3.5                                                      56       824   1872   3.9                                                      66       849   1886   3.3                                                      66       859   1859   2.5                                                      80       843   1932   3.7                                                      80       831   1927   3.9                                                      100      870   2225   3.7                                                      100      763   1759   5.9                                                      100      768   1742   4.6                                                      154      705   1704   5.3                                                      154      756   1845   4.9                                                      199      786   1976   4.6                                                      199      809   2047   3.9                                                      199      857   2308   4.5                                                      199      870   2402   3.7                                                      253      868   2449   3.7                                                      253      865   2506   4.3                                                      299      884   2360   4.5                                                      299      911   2563   3.7                                                      1002     896   2548   4.1                                                      1002     894   2644   4.1                                       2-ethylhexylamine                                                                             0        898   1330   7.77                                                     0        919   1197   5.26                                                     5       1521   2351   2.85                                                     5       1525   2269   2.07                                                     10      1730   2842   1.70                                                     10      1698   2756   2.13                                                     20      1831   3129   2.06                                                     20      1842   3042   1.51                                                     50      1927   3818   1.90                                                     50      1941   3742   1.68                                                     100     1897   4095   1.79                                                     100     1934   4011   1.84                                                     200     1892   3686   1.78                                                     200     1884   3811   2.08                                                     300     1745   4201   3.97                                                     300     1785   4410   3.48                                                     400     1799   3995   2.92                                                     400     1862   3852   3.06                                                     500     1847   3825   2.54                                                     500     1852   3824   1.31                                                     600     1860   3827   3.39                                                     600     1836   3642   2.54                                                     1000    1807   3628   3.49                                                     1000    1806   3683   2.76                                      N,N-diisopropylethylamine                                                                     0       1014   1566   7.43                                                     0       1045   1598   6.79                                                     0       1041   1366   5.60                                                     0       1061   1414   5.89                                                     0       1038   1426   6.01                                                     0       1047   1470   6.41                                                     5       1149   1673   5.72                                                     5       1161   1704   5.67                                                     10      1281   1746   4.06                                                     10      1288   1737   4.31                                                     20      1364   1900   3.71                                                     20      1381   1932   4.23                                                     50      1341   1973   3.68                                                     50      1359   2022   4.18                                                     100     1423   2245   4.47                                                     100     1434   2285   4.37                                                     200     1497   2634   4.99                                                     200     1505   2619   5.02                                                     300     1450   2789   5.89                                                     300     1468   2878   5.66                                                     400     1494   2990   5.56                                                     400     1513   3010   5.80                                                     600     1487   3131   6.30                                                     600     1501   3127   6.42                                      N,N-dimethyloctylamine                                                                        0        967   1211   4.97                                                     0        991   1253   5.01                                                     0        997   1239   4.86                                                     0       1079   1461   4.26                                                     0       1116   1552   4.77                                                     0       1133   1608   5.18                                                     0       1141   1525   4.51                                                     0       1155   1597   5.00                                                     0       1075   1432   4.15                                                     5       1366   2077   3.30                                                     5       1396   2127   3.72                                                     10      1486   2527   3.75                                                     10      1527   2632   3.44                                                     20      1621   2771   2.75                                                     20      1626   2826   3.32                                                     50      1677   3083   3.92                                                     50      1657   3212   4.35                                                     50      1660   3166   4.30                                                     100     1613   3052   4.30                                                     100     1602   3016   3.89                                                     150     1601   3229   4.15                                                     150     1595   3169   4.46                                      aniline        0        911   1224   7.31                                                     0        983   1321   7.31                                                     0        966   1217   8.14                                                     0        954   1088   5.35                                                     10       954   1331   7.91                                                     10       977   1328   7.77                                                     10       978   1362   7.61                                                     20      1055   1533   6.96                                                     20      1067   1563   6.86                                                     20      1072   1552   7.05                                                     50      1312   2213   6.60                                                     50      1345   2271   6.68                                                     50      1357   2319   6.52                                                     100     1564   3147   6.18                                                     100     1551   3091   5.98                                                     100     1555   3134   5.88                                                     100     1563   3101   5.98                                                     200     1620   3616   6.15                                                     200     1686   3708   6.75                                                     200     1674   3675   6.73                                                     200     1656   3613   6.90                                                     500     1669   3758   6.83                                                     500     1488   3421   7.67                                                     500     1472   3409   7.67                                                     500     1420   3415   7.58                                      benzylamine    0        783   1031   7.06                                                     0        771    970   6.44                                                     0        794    973   5.80                                                     7.9     1421   2039   2.97                                                     7.9     1409   1942   2.38                                                     7.9     1426   1954   2.34                                                     15      1355   2022   3.71                                                     15      1352   1805   2.41                                                     15      1336   1792   2.40                                                     25.6    1315   1885   3.51                                                     25.6    1304   1670   2.11                                                     25.6    1298   1676   2.34                                      pyridine       0       1041   1266   5.4                                                      0       1038   1246   4.6                                                      0       1034   1194   4.2                                                      0       1034   1188   4.0                                                      5.1     1059   1233   3.7                                                      5.1     1082   1232   3.4                                                      5.1     1052   1199   3.5                                                      10.3    1086   1241   3.3                                                      10.3    1070   1215   3.3                                                      10.3    1077   1216   3.1                                                      20.2    1264   1536   2.8                                                      20.2    1246   1500   2.6                                                      20.2    1266   1506   2.3                                                      34.8    1437   1806   2.1                                                      34.8    1437   1796   1.9                                                      34.8    1449   1805   1.8                                                      49.5    1521   1942   1.7                                                      49.5    1510   1934   1.7                                                      49.5    1509   1926   1.4                                                      65.5    1631   2271   2.4                                                      65.5    1629   2252   2.2                                                      65.5    1624   2226   2.0                                                      80.3    1719   2367   1.1                                                      80.3    1714   2355   1.1                                                      80.3    1715   2362   1.1                                                      99.8    1786   2542   1.1                                                      99.8    1781   2532   1.1                                                      99.8    1769   2516   1.1                                                      124.8   1793   2677   1.3                                                      124.8   1794   2709   1.2                                                      124.8   1833   2712   1.3                                                      149.8   1739   2426   1.0                                                      149.8   1737   2352   0.6                                                      149.8   1729   2365   0.5                                                      174.8   1726   2353   0.5                                                      174.8   1737   2340   0.4                                                      174.8   1739   2358   0.4                                                      224.7   1740   2429   1.1                                                      224.7   1733   2393   1.0                                                      224.7   1719   2400   1.0                                                      278.3   1740   2456   1.0                                                      278.3   1749   2458   0.9                                                      278.3   1755   2450   0.7                                                      414     1734   2484   1.2                                                      414     1733   2469   1.1                                                      414     1718   2437   0.9                                                      600     1670   2432   1.6                                                      600     1691   2418   1.3                                                      600     1682   2388   1.2                                                      802     1649   2366   1.5                                                      802     1646   2346   1.4                                                      802     1648   2334   1.3                                                      1002    1607   2336   1.9                                                      1002    1599   2335   2.0                                                      1002    1619   2291   1.6                                                      1498    1637   2525   2.7                                                      1498    1607   2493   2.6                                                      1498    1613   2503   2.5                                                      1995    1548   2436   3.4                                                      1995    1536   2400   3.2                                                      1995    1543   2405   3.3                                                      2496    1379   2037   3.6                                                      2496    1385   2016   3.3                                                      2496    1398   2015   3.2                                                      2990    1331   1998   4.0                                                      2990    1325   1946   3.8                                                      2990    1319   1933   3.8                                                      3500    1235   1822   4.5                                                      2500    1266   1852   4.1                                                      2500    1259   1828   4.1                                                      4000    1198   1774   4.8                                                      4000    1204   1739   4.4                                                      4000    1198   1742   4.5                                       quinoline      0        936   1152   5.94                                                     0        937   1087   4.91                                                     0        894   1002   4.85                                                     0        990   1288   5.94                                                     6.6     1178   1392   3.44                                                     6.6     1183   1535   4.41                                                     6.6     1192   1442   3.45                                                     12.6    1419   1777   2.65                                                     12.6    1392   1702   2.57                                                     12.6    1372   1681   2.43                                                     24.9    1534   2002   2.31                                                     24.9    1498   1978   1.75                                                     24.9    1542   1965   2.07                                                     49.2    1723   2801   3.91                                                     49.2    1731   2755   3.99                                                     49.2    1749   2795   3.97                                                     74.3    1774   2718   2.38                                                     74.3    1765   2714   2.58                                                     74.3    1727   2579   2.13                                                     100.1   1819   2680   1.34                                                     100.1   1869   2790   1.75                                                     100.1   1852   2758   1.80                                                     100.1   1823   2730   1.30                                                     100.1   1859   2733   1.31                                      benzonitrile   0        872   1199   6.79                                                     0        883   1193   6.85                                                     5       1187   1706   4.58                                                     5       1197   1648   3.90                                                     10      1277   1965   4.78                                                     10      1267   1960   4.70                                                     20      1354   2429   5.18                                                     20      1380   2189   4.30                                                     50      1440   2518   4.30                                                     50      1459   2394   3.90                                                     100     1435   2704   5.32                                                     100     1438   2726   5.45                                                     200     1284   2758   7.55                                                     200     1325   2459   6.36                                                     200     1362   2584   5.51                                                     200     1418   2552   5.01                                                     250     1386   2476   5.22                                                     250     1390   2434   4.98                                      ______________________________________                                    

From the test results given in the Table, utilizing representative examples of amines according to the invention, the improvements of the operating condition performance, taken from actual measurements of the laboratory bench test system as well as calculated values for fluid film heat transfer coefficients (h_(o)) are shown. Additionally, the absorber power load increases are shown as are the significant decreases in solution subcooling at the operating conditions. Calculated values of film heat transfer coefficients (h_(o)) are also increased. 

We claim:
 1. A water vapor absorption cycle cooling and/or heating system containing an aqueous working fluid consisting essentially of water as the solvent and comprising between about 30% and about 85%, by weight, of a metal compound selected from the group consisting of lithium bromide, lithium chloride, lithium iodide and mixtures of two or more thereof, sodium hydroxide, potassium hydroxide and mixtures of said hydroxides, and an effective additive amount of at least 2 parts per million, by weight, of an aliphatic, cycloaliphatic, heterocyclic, or aromatic amine having between 4 and 20 carbon atoms, capable of increasing the rate of water vapor sorption of said working fluid.
 2. A system of claim 1 comprising single or double effect absorption apparatus and wherein said metal compound comprises lithium bromide.
 3. A system of claim 2 wherein said amine comprises a primary, secondary or tertiary aliphatic or cycloaliphatic amine having between 6 and 12 carbon atoms.
 4. A system of claim 2 wherein said amine comprises a cycloaliphatic amine.
 5. A system of claim 2 wherein said amine comprises an aromatic amine.
 6. A system of claim 5 wherein said aromatic amine has between 4 and 12 carbon atoms.
 7. A system of claim 6 wherein said aromatic amine is a halogen substituted amine.
 8. A system of claim 6 wherein said amine is quinoline or isoquinoline.
 9. A system of claim 6 wherein said amine is benzylamine.
 10. A system of claim 2 wherein said amine is aniline or a substituted aniline.
 11. A system of claim 10 wherein said substituted aniline is a halogen substituted aniline.
 12. A system of claim 2 wherein said amine is an isomer of diaminocyclohexane.
 13. A system of claim 2 wherein said amine is octylamine.
 14. A system of claim 2 wherein said amine is nonylamine.
 15. A system of claim 2 wherein said amine is decylamine.
 16. A system of claim 2 wherein said amine is ethylhexyl amine.
 17. A system of claim 2 where said amine is 2-ethylhexylamine.
 18. A system of claim 3 wherein said amine is dimethylhexylamine.
 19. A system of claim 3 wherein said amine is N,N-diisopropylethylamine.
 20. A system of claim 3 wherein said amine is N,N-dimethyloctylamine.
 21. A system of claim 3 wherein said amine is N,N-diethyloctylamine.
 22. A system of claim 3 wherein said amine is a saturated heterocyclic amine.
 23. A system of claim 22 wherein said amine is piperidine.
 24. A system of claim 23 wherein said piperidine is methyl substituted.
 25. A system of claim 23 wherein said piperidine is fluoro substituted.
 26. A system of claim 22 wherein said amine is pyrrolidine.
 27. A system of claim 2 wherein said amine is an unsaturated heterocyclic amine.
 28. A system of claim 27 wherein said amine is pyridine.
 29. A system of claim 28 wherein said pyridine is methyl or fluoro substituted.
 30. A system of claim 27 wherein said amine is pyrrole.
 31. A system of claim 30 wherein said pyrrole is methyl or fluoro substituted.
 32. A system of claim 27 wherein said amine is pyrroline.
 33. A system of claim 2 wherein said amine is a methyl diaminopentane.
 34. A system of claim 2 wherein said working fluid contains a mixture of two or more of said amines.
 35. A system of claim 1 wherein said amine is a liquid at temperatures of between about 30° C. and about 100° C.
 36. A system of claim 1 wherein said additive amount is between 2 ppm and about 20,000 ppm, by weight.
 37. A system of claim 2 wherein said additive amount is between 2 ppm and about 10,000 ppm, by weight.
 38. A system of claim 2 wherein said aqueous working fluid contains lithium bromide and one or more salts selected from the group consisting of ZnCl₂, ZnBr₂, MnCl₂, MnBr₂, MgCl₂, MgBr₂, SrCl₂, SrBr₂, CaCl₂, CaBr₂, FeCl₂, FeBr₂, LiCl, LiI, LiNO₂, LiNO₃, LiSCN and LiClO₃.
 39. A single or double effect water vapor absorption cycle cooling and/or heating system containing an aqueous working fluid consisting essentially of water as the solvent and having between about 40% and about 85% by weight lithium bromide, and an effective additive amount of at least 2 parts per million, by weight, of a primary, secondary or tertiary aliphatic, cycloaliphatic, heterocyclic or aromatic amine capable of increasing the rate of water vapor sorption of said working fluid.
 40. A system of claim 39 wherein said amine is a liquid at temperatures of between about 30° C. and about 100° C.
 41. A system of claim 39 wherein said amine comprises an aliphatic amine having between 4 and 20 carbon atoms.
 42. A system of claim 39 wherein said amine comprises a cyclohexylamine.
 43. A system of claim 39 wherein said amine comprises an aromatic amine.
 44. A system of claim 43 wherein said aromatic amine has between 4 and 12 carbon atoms.
 45. A system of claim 39 wherein said amine is a heterocyclic amine.
 46. A system of claim 39 wherein said amine is aniline or a substituted aniline.
 47. A system of claim 39 wherein said amine is 2-ethylhexyl amine.
 48. A system of claim 39 wherein said amine is dimethyloctylamine.
 49. A system of claim 39 wherein said amine is piperidine or substituted piperidine.
 50. A system of claim 39 wherein said amine is pyrrolidine.
 51. A system of claim 39 wherein said amine is pyrrole.
 52. A system of claim 39 wherein said amine is diisopropylethylamine.
 53. A system of claim 39 wherein said amine is pyridine or a substituted pyridine.
 54. A system of claim 39 wherein said amine is quinoline or isoquinoline.
 55. A system of claim 39 wherein said amine is benzylamine.
 56. A system of claim 39 wherein said amine comprises a diamine.
 57. A system of claim 39 wherein said working fluid contains a mixture of two or more amines.
 58. A system of claim 39 wherein said effective additive amount is between 2 ppm and about 20,000 ppm, by weight.
 59. A system of claim 39 wherein said aqueous working fluid includes, in addition to said lithium bromide, one or more salts selected from the group consisting of ZnCl₂, ZnBr₂, MnCl₂, MnBr₂, MgCl₂, MgBr₂, SrCl₂, SrBr₂, CaCl₂, CaBr₂, FeCl₂, FeBr₂, LiCl, LiI, LiNO₂, LiNO₃, LiSCN and LiClO₃.
 60. In operation of an absorption cycle cooling and/or heating system including an absorber containing an aqueous metal salt or metal hydroxide absorption solution for absorbing water vapor therein wherein water is the only substantial solvent and said metal salt is an alkali metal halide, and said metal hydroxide is sodium hydroxide, potassium hydroxide or mixtures of said hydroxides, a method of improving the rate of water vapor absorption of said absorption solution comprising adding thereto an effective additive amount of between 2 and about 20,000 parts per million, by weight, of a primary, secondary or tertiary aliphatic, cycloaliphatic, heterocyclic or aromatic amine capable of increasing said rate of water vapor absorption.
 61. A method of claim 60 wherein said amine is a liquid at temperatures of between about 30° C. and about 100° C.
 62. A method claim 60 wherein said amine comprises an aliphatic amine having between 4 and 20 carbon atoms.
 63. A method of claim 60 wherein said amine comprises an aromatic amine having between 6 and 12 carbon atoms.
 64. A method of claim 60 wherein said amine is a cyclohexylamine.
 65. A method of claim 60 wherein said amine is aniline or a substituted aniline.
 66. A method of claim 60 wherein said amine is a diamine.
 67. A method of claim 60 wherein said amine is 2-ethylhexylamine.
 68. A method of claim 60 wherein said amine is dimethyloctylamine.
 69. A method of claim 60 wherein said amine is piperidine or substituted piperidine.
 70. A method of claim 60 wherein said amine is pyrrolidine.
 71. A method of claim 60 wherein said amine is pyrrole.
 72. A method of claim 60 wherein said amine is diisopropylethylamine.
 73. A method of claim 60 wherein said amine is benzyl amine.
 74. A method of claim 60 wherein said amine is pyridine or a substituted pyridine.
 75. A method of claim 60 wherein said alkali metal halide is lithium bromide.
 76. A method of claim 75 wherein said aqueous working fluid includes, in addition to said lithium bromide, one or more salts selected from the group consisting of ZnCl₂, ZnBr₂, MnCl₂, MnBr₂, MgCl₂, MgBr₂, SrCl₂, SrBr₂, CaCl₂, CaBr₂, FeCl₂, FeBr₂, LiCl, LiI, LiNO₂, LiNO₃, LiSCN and LiClO₃.
 77. A system of claim 75 wherein said additive amount is between 2 ppm and about 10,000 ppm, by weight.
 78. A system of claim 1 wherein said metal compound is sodium hydroxide, potassium hydroxide or mixtures thereof and said amine is a saturated heterocyclic amine.
 79. A system of claim 78 wherein said amine is piperidine.
 80. A system of claim 79 wherein said piperidine is methyl or fluoro substituted.
 81. A system of claim 78 wherein said amine is pyrrolidine.
 82. A system of claim 1 wherein said metal compound is sodium hydroxide, potassium hydroxide or mixtures thereof and said amine is an unsaturated heterocyclic amine.
 83. A system of claim 82 wherein said amine is pyridine.
 84. A system of claim 83 wherein said pyridine is methyl or fluoro substituted.
 85. A system of claim 82 wherein said amine is pyrrole.
 86. A system of claim 85 wherein said pyrrole is methyl or fluoro substituted.
 87. A system of claim 82 wherein said amine is pyrroline.
 88. A system of claim 1 wherein said metal compound is sodium hydroxide, potassium hydroxide or mixtures thereof and said amine is quinoline or isoquinoline.
 89. A system of claim 1 wherein said metal compound is sodium hydroxide, potassium hydroxide or mixtures thereof and said amine is benzylamine. 